Powder-coating equipment is known from the European patent application EP 0,718,043 A1 wherein a conveying airflow generates a partial vacuum in a vacuum zone of an injector and thereby sucks powder out of a container and moves it into a powder line. Downstream of the vacuum zone, supplemental air is supplied through a supplemental-air intake to the flow of conveying air and powder in order to implement a predetermined flow of total air.
European patent 0,412,289 B1 discloses electrostatic powder coating equipment having an injector fed with conveying and with supplemental air. The supplemental air can be conveyed as control air into the injector vacuum zone.
German Offenlegungsschrift DE 44 19 987 A1 discloses an injector/conveyor system to move coating powder, having a suction pipe connected to the injector vacuum zone and running downward into a powder container, whereby powder is sucked from this container into the vacuum zone. Compensating air is fed to the suction pipe end located remote from the vacuum zone to compensate for fluctuations in the suction amplitude. As shown by U.S. Pat. No. 3,746,254, the powder container can also be mounted above the injector vacuum zone, instead of underneath, whereby the powder suction aperture is located above the vacuum zone.
European patent application EP 0,769,327 A1 discloses powder coating equipment wherein the injector is located at the lower end of a pipe which is immersible into a powder container in order to convey powder from it.
The present invention encompasses all the above embodiments and is not restricted to any particular embodiment.
It is known with respect to powder coating equipment to cleanse the powder line of deposited powder particles from time to time, usually with a hose and spray apparatus, This procedure is required to preclude unchecked discharge of deposited, old powder particles which would interfere with coating the surface of an object. Ordinarily, compressed air is connected to the injector to flush the powder hose and the spray apparatus by being blown through the injector and the powder hose and spray apparatus. This known flushing procedure incurs a drawback in that the flushing air not only flows to the spray apparatus, but also divides inside the injector into other lines communicating with it. The known systems suffer from a further drawback in that the powder coating operation must be stopped when cleansing with flushing air and that later the conveying air and any supplemental air must be readjusted to the desired pressure levels and rates of conveyed powder. While powder deposits in the powder hose can be markedly reduced by using a hose made of an appropriate material, nevertheless, when dealing with great hose lengths, the quantity of deposited powder particles remains comparatively high.
The object of the invention is to achieve very high quality coating of a large series of objects without interfering with or interrupting this mass production on account of cleansing procedures or adjustments of the spray coating equipment. Illustratively, the invention enables mass-coating of automobile bodies with a surface quality as good as presently offered by liquid enamel. Accordingly, the object of the present invention is to place the highest requirements on powder coating quality regarding object adhesion, sealing of the powder coating after being baked onto the object, extreme uniformity and smoothness in the coating. The related method and equipment shall offer very high reliability in permanent operation.